Those drilled pipes are actually serving the exact opposite purpose. I have two 300 gph power heads behind the background pushing forward to create some water movement in the tank as I didn't want any visual equipment. Even so the sand still fell thru the holes In a trial run every time I had to turn the power heads off so I layed out a layer of vinyl "sun screen" from Home Depot that cost about $2 to cover the whole tank twice over. It does restrict some flow but still seems to get the job done.